Involvement of Hydrogen Peroxide in Topoisomerase Inhibitor β-lapachone-Induced Apoptosis and Differentiation in Human Leukemia Cells

β-Lapachone a novel topoisomerase inhibitor, has been found to induce apoptosis in various human cancer cells. In this study we report that a dramatic elevation of hydrogen peroxide (H2O2) in human leukemia HL-60 cells following 1 μM β-lapachone treatment and that this increase was effectively inhibited by treatment with antioxidant N-acetyl-image-cysteine (NAC), ascorbic acid, alpha-tocopherol. NAC strongly prevented β-lapachone-induced apoptotic characteristics such as DNA fragmentation and apoptotic morphology. However, treatment of HL-60 cells with another topoisomerase inhibitor camptothecin (CPT) did not induce H2O2 production as compared to untreated cells. NAC also failed to block CPT-induced apoptosis. Correlated with these findings, we found that cancer cell lines K562, MCF-7, and SW620, contained high level of intracellular glutathione (GSH), were not elevated in H2O2 and were resistant to apoptosis after treatment with β-lapachone. In contrast, cancer cell lines such as, HL-60, U937, and Molt-4 which have lower level of GSH, were readily increased of H2O2 and were sensitive to this drug. Furthermore, ectopic overexpression of Bcl-2 in HL-60 cells also attenuated β-lapachone-induced H2O2 and conferred resistance to β-lapachone-induced cell death. β-Lapachone at the concentration as low as 0.25 μM effectively induced HL-60 cells to undergo monocytic differentiation, as evidenced by CD14 antigenicity and α-naphthyl acetate esterase activity. Again, the β-lapachone-induced monocytic differentiation was suppressed by NAC. These results suggest that intracellular H2O2 generation plays a crucial role in β-lapachone-induced cell death and differentiation.